Add irc_timezone to testing.yml to fix dev build

Vagrant provisioning currently fails without irc_timezone set in
vars/testing.yml.  This is probably due to changes introduced in
al3x/sovereign#300 to permit the znc timezone to be configured.  The
file vars/users.yml already has a TODO entry for irc_timezone.

vars/testing.yml

 irc_quitmsg: Bye
 irc_password_hash: "310c5f99825e80d5b1d663a0a993b8701255f16b2f6056f335ba6e3e720e57ed" #foo
 irc_password_salt: "YdlPM5yjBmc/;JO6cfL5"
+irc_timezone: "America/New_York" #Example: "America/New_York"
 
 # mailserver
 mail_db_password: testPassword